Oleander (Nerium oleander L.) shrubs presenting mottling, leaf tip and margin scorch, short internodes, defoliation, and branch dieback were observed at different localities in the Central Valley in Costa Rica. Severity of the symptoms ranged widely, and most plants showed both diseased and healthy branches. In severe cases, entire sections of the plant were defoliated. Symptoms resembled those described for oleander leaf scorch (OLS) caused by the bacterium Xylella fastidiosa in the United States (3). This bacterium has been reported in coffee and citrus plants in Costa Rica. Sixty plants from five different places were sampled and tested using ELISA (Agdia Inc., Elkhart, IN) against X. fastidiosa. Thirty-five plants showed absorbance mean value of duplicate wells greater than the mean of control wells plus three times the standard deviation, and therefore were considered positive. Thirty-three of the sixty samples were processed for an immunofluorescence assay modified from Carbajal et al. (1) with antibody to X. fastidiosa (Agdia Inc.). Thirteen samples showed fluorescent rod-shaped bacilli with morphology similar to those observed from a pure culture of X. fastidiosa obtained from coffee. Ten of these thirteen samples were positive by ELISA. DNA extracts (2) from three of the oleander plants with high ELISA absorbance values were tested by nested PCR with primer pair 272-1/272-2 followed by the pair 272-1 int/272-2 int (4). Two of the samples were positive for the bacterium and one of the PCR products was cloned and sequenced in both directions (GenBank Accession No. EU009615). The negative (PCR mix) and positive (pure culture of X. fastidiosa isolated from grapevine) controls for nested-PCR were indeed negative and positive, respectively. The BLAST program was used to compare the sequence to the nucleotide collection (nr/nt) and Microbe Assembled Genomes databases in GenBank. All matches corresponded to X. fastidiosa sequences. The sequence showed 97% similarity with strains Found-4 (coffee strain from Brazil) and Found-5 (citrus strain from Brazil) and 96% similarity with strain Ann-1 from oleander in California. On the basis of serological, microscopic, and molecular detection of X. fastidiosa from oleander exhibiting symptoms of OLS similar to those reported in the literature, this pathogen likely is causing the symptoms we observed in Costa Rica.
References: (1) D. Carbajal et al. Curr. Microbiol. 49:372, 2004. (2) M. J. Green et al. Plant Dis. 83:482, 1999. (3) Q. Huang et al. Plant Dis. 88:1049, 2004. (4) M. R. Pooler and J. S. Hartung. Curr. Microbiol. 31:377, 1995.